1. Field of the Invention
The invention relates to novel bleach precursors, peracids generated therefrom and use of these materials in detergent compositions.
2. The Prior Art
It is well known that active oxygen-releasing compounds are effective bleaching agents. These compounds are frequently incorporated into detergent compositions for stain and soil removal. Unlike the traditional sodium hypochlorite bleaches, oxygen-releasing compounds are less aggressive and thus more compatible with detergent compositions. They have, however, an important limitation; the activity of these compounds is extremely temperature dependent. Thus, oxygen-releasing bleaches are essentially only practical when the bleaching solution is heated above 60.degree. C. At a temperature of just 60.degree. C., extremely high amounts of the active oxygen-releasing compounds must be added to the system to achieve any bleach effect. Although this would indicate the desirability of high temperature operation, high temperatures are both economically and practically disadvantageous.
At bleach solution temperatures below 60.degree. C., the active oxygen-releasing compounds are rendered much less effective regardless of their level in the system. With respect to bleaching of laundry in automatic household washing machines, it must be noted that these machines are normally operated at wash-water temperatures below 60.degree. C. Consequently, there has developed a need for substances which promote release of active oxygen at temperatures below 60.degree. C. These substances are generally referred to in the art as bleach precursors, although they have also been called promoters and activators. Normally, bleach precursors are used in conjunction with persalts capable of releasing hydrogen peroxide in aqueous solution, perborate being the most widely used persalt.
Typically, the precursor is a reactive compound such as a carboxylic acid ester that in alkaline detergent solution containing a source of hydrogen peroxide, e.g. a persalt, will generate the corresponding peroxy acid. The reaction involves nucleophilic substitution onto the precursor by hydroperoxy anions (HOO.sup.-) and is facilitated by precursors having good leaving groups. Often the reaction is referred to as a perhydrolysis.
Early patents in the area of precursor chemistry include U.S. Pat. No. 3,256,198 (Matzner) and U.S. Pat. No. 3,272,750 (Chase) each of which suggest the use of organic carbonate esters as bleach aids. British Pat. No. 836,988 (Davies et al.) and British Pat. No. 864,798 (Hampson et al.) were forerunners disclosing the use of aliphatic carboxylic acid esters as adjuncts for accelerating the bleaching of persalts such as sodium perborate or percarbonate.
U.S. Pat. No. 4,283,301 (Diehl) discloses a peroxygen bleach and a precursor of the general formula: ##STR1## wherein R is an alkyl chain containing from 5 to 13 carbon atoms, R.sup.2 is an alkyl chain containing from 4 to 24 carbon atoms and each Z is a leaving group as defined therein.
U.S. Pat. No. 4,412,934 (Chung et al.) reports compositions incorporating bleach precursors of the general formula: ##STR2## wherein R is an alkyl group containing from 5 to 18 carbon atoms and L is a leaving group.
Similar disclosures are found in U.S. Pat. No. 4,486,327 (Murphy et al.), EP No. 0 098 129 (Hardy et al.), EP No. 0 106 584 (Hartman), EP No. 0 106 634 (Chung et al.), EP No. 0 120 591 (Hardy et al.), EP No. 0 163 331 (Burns et al.), EP No. 0 166 571 (Hardy et al.), EP No. 0 185 522 (Fong et al.), EP No. 0 170 386 (Burns et al.), EP No. 0 153 222 (Moyne et al.), EP No. 0 153 223 (Moyne et al.), and EP No. 0 202 698 (Nollet et al.). Among the preferred leaving groups are those having solubilizing functionality including sufonic, sulfuric, carboxylate and quaternary ammonium salt groups.
A typical precursor within the concept of the aforedescribed patents is sodium n-nonanoyloxbenzene sulfonate presently commercialized as a component of a branded detergent. This sulfonate, in combination with sodium perborate, effectively releases peroxygen fragments upon perhydrolysis, as well as sodium 4-sulfophenol. Once released, the p-sulfophenol fragment unfortunately provides no additional fabric washing benefit.
Esters such as sodium n-nonanoyloxybenzene sulfonate are reported to require greater than stoichiometric amounts of alkaline hydrogen peroxide. For example, U.S. Pat. No. 4,536,314 (Hardy et al.) discloses hydrogen peroxide/activator ratios ranging from greater than 1:5:1 to 10:1. High peroxide ratios are necessary with these activators to ensure high rates of peracid formation and to account for the unavoidable depletion of peroxide by natural soils. These high ratios are economically wasteful.
U.S. Pat. No. 3,686,127 (Boldingh et al.) recognizes the shortcomings of precursors whose leaving groups provide no additional fabric washing benefit. Therefore, the patent suggests use of alkylated sulfophenol carboxylic esters which release leaving groups that provide detergent and emulsifying properties. However, with this modification to the leaving group structure, the yield of peracid falls to essentially non-useful levels. For instance, sodium 2-acetoxy-5-hexylbenzene-sulfonate yields 43% peracid after 5 minutes but the unsubstituted derivative yields 80% peracid. Presumably, unfavorable steric or electrostatic interactions arising from the alkyl substituents retard the rate of perhydrolysis.
U.S. Pat. No. 4,397,757 (Bright et al.) reports that having quaternary ammonium groups on the precursor is advantageous because it allows precursor and intermediate species to substantively attach onto srfaces undergoing bleaching, e.g. fabric surfaces. Substativity was said to lead to enhanced stain removal, particularly at low temperature. A drawback of this technology is the expense in preparing the precursors; the synthesis involves several steps and requires excess reagent. Starting materials are also not readily available.
While the aforementioned precursors have all been reported effective at stain removal, there is still a need for more efficient systems. Stain removal efficiency may be improved either by a precursor that generates equivalent bleach at a lower precursor molar level or operates at lower levels of hydrogen peroxide source. Not only do lower levels of peroxide source or precursor provide better economics, theyalso permit increased flexibility in detergent formulation.
Consequently, it is an object of the present invention to provide a detergent-bleach composition with a precursor that permits bleaching over a wide temperature range including that of under 60.degree. C.
It is another object of the present invention to provide certain novel bleach precursors which have hitherto not been described in the art.
A further object of the present invention is to provide a precursor having a group capable of imparting additional benefits to treated substances including that of detergency and/or fabric softening while still achieving high peracid generating levels.
Another object of the present invention is to provide a precursor that can be economically synthesized from readily available starting materials and in a minimum number of synthetic steps.
A final object of the present invention is to provide novel peroxy acids generated from the bleach precursors by perhydrolysis with hydrogen peroxide or persalts.